Direct iron and steelmaking

ABSTRACT

Solid state iron oxide reduction in a gas-solid reduction zone is combined with continuous melting of the hot solid reduced iron in a fuel-fired gas-solid-liquid melting zone within a rotary furnace. The process includes direct pneumatic transfer of the hot reduced iron by carrier gases through a transfer duct incorporating an injection lance nozzle projecting a jet of hot reduced iron downwards into the metal bath within the melting zone. Oxygen is also introduced into the hot gas stream at selected locations in the melting zone for post-combustion with carbon monoxide generated by a carbon boil and combustion with other combustible gases prior to exit from the rotary furnace, thereby furnishing heat for melting. The hot gas stream is then utilized to provide a significant part of the heat requirement for reduction, prior to exhausting into the atmosphere. A feature is distributing the hot solid reduced iron laterally and longitudinally within the melting zone to enhance heat transfer for melting, including a preferred embodiment comprising continually traversing the jet of carrier gases and hot reduced iron longitudinally forwards and backwards . The invention embraces a broad range of known solid-state reduction processes, classified either as: Group A. those employing gases within a gravity contact-supported or fluidized moving bed at substantial pressures of 1-5 atmospheres; or Group B. solid carbonaceous reductants in a rotary kiln or rotary hearth conducted at near ambient atmospheric pressure. Combustibles in the exhaust gases and unnecessary fume generation caused by direct injection of oxygen into the bath are avoided, as problems endemic to known electric-arc and converter steelmaking technologies. A preferred embodiment applied to Group A reduction includes in situ reforming of a major portion of the hydrocarbons applied as reducing gases in the reduction zone, in combination with reforming a minor portion by partial oxidation with oxygen. The process includes various other preferred features which significantly improve energy requirements, production rates, yields, costs and control of the liquid iron and steel product composition and quality in relation to the prior art.

[0001] The invention relates to the manufacturing of iron and steel andmore particularly, to a process for direct iron and steelmaking.

[0002] My U.S. Pat. No. 5,542,963 describes a process for direct ironand steelmaking featuring the combination of solid-state iron oxidereduction by pressurized hot reducing gases followed by continuousmelting of the hot reduced iron. This invention comprises a modifiedprocess extended to be more versatile, including several improvementsand additions. This application is a continuation-in-part of co-pendingapplication No. 08/916395.

[0003] There are a large number of known processes and variationsthereof for accomplishing solid-state iron oxide reduction, all of whichachieve the object of producing direct reduced iron, known as DRI orsponge iron, as the end product. These may conveniently be divided intothe following two groups:

[0004] Group A: Solid-state reduction processes employing pressurizedhot reducing gases percolated through a gravity contact-supported orfluidized columnar moving bed of iron oxide particles, pellets or lumps,wherein the pressurized reducing gases comprise recirculated top gasesenriched by externally reformed hydrocarbons and/or directly introducedhydrocarbons and the in-bed pressure of the reducing gases at productdischarge is substantial, typically in the range of 1-5 atmospheres; and

[0005] Group B: Solid-state reduction processes employing coal or othersolid carbonaceous reductant, either mixed with iron oxide pellets orlumps as discrete particles, or as a constituent of agglomerated(pelletized) iron oxides, traversing along elongated and relativelyshallow moving beds within rotary kilns or carried upon rotary ortraveling hearths, and which include a non-recirculated heating gasphase over the bed, as well as reducing gas phase within the bedgenerated by in-bed reaction of the coal, and wherein the process gaspressure at product discharge is close to zero relative to ambientatmospheric pressure.

[0006] Group A processes for DRI production include, for example,MIDREX, HYL, PUROFER, NIPPON STEEL-DR, and AREX-SBD featuring gravitycontact-supported descending moving beds within shaft furnace reactorsand the FIOR, FINMET, SPIREX, CIRCORED and CIRCOFER processes influidized beds and the iron carbide processes, either with fluidized orgravity contact-supported beds.

[0007] Group B processes include SL/RN, DRC, KRUPP-CODIR and ACCAR (withcoal) processes employing discrete particle iron-coal mixtures heatedwithin rotary kilns. The FASTMET and INMETCO processes employ pelletizedmixtures of fine particulate iron oxide and coal, and COMET alternatelayers or iron oxides and a coal/limestone mixture, heated upon. rotaryhearths.

[0008] An overall object of the present invention is to combinein-process features from known processes in these two groupings withinthe art of solid-state iron ore reduction together with continuous metalmelting, comprising a continuous sequence of process steps to produceliquid iron and steel directly from iron oxides, to realize higheroutput with improved control of product composition and quality, lowerenergy requirements, higher metal yield with lower material losses, andlower discharge of environmental pollutants than by currently knownprocesses or combinations of processes.

[0009] When considering the solid-state reduction process stage, it isnot notable that the ACCAR process, when operated with only natural gasor fuel oil, is an exception outside the two above groupings, because itoperates near atmospheric pressure without solid carbonaceous reductant.Between 1967 and 1977, in pilot and demonstration rotary kiln plantsoperated at near-atmospheric pressures, it was shown that hydrocarbonsin the form of natural gas or oil, when injected directly into a hot bedof iron oxide pellets, were reformed into reducing gases (CO+H₂) withinthe bed itself, obviating the need for external reforming. This work wassummarized in “Direct Reduced Iron-Technology and Economics ofProduction and Use”, Iron and Steel Society, AIME, 1980, pp. 87-90. Onlyafter about ten or more years was this conceptual breakthrough alsoapplied to Group A processes, for example, AREX technology as analternative to other shaft furnace technologies which use externallyreformed gases for reduction. A wide range of reducing gas makeups aretherefore workable, appearing necessary only that approximately suitabletemperatures and ratios between H, C and 0 be maintained in the reducinggas, for sustainable solid-state reduction to metallic iron to proceed.This latitude allows the selection of features for solid-state ironoxide reduction circuits to be more freely focused upon such objects aslow process energy requirements, high production rate, low volumes ofwaste gases containing less particulates and unburned combustibles,improved control of product composition, simplicity and low costs.

[0010] The various oxygen converter and electric - arc furnace processesdominate current commercial steelmaking practice, but share a commonproblem of unburned combustibles CO and H₂ contained in the off-gases.The known bath smelting processes also share this difficulty. Thedevelopment of post-combustion technology has mitigated this problem,but the post-combustion degree (PCD) continues to vary widely duringdifferent stages of each heat of steel and substantial excess oxygen viamultiple furnace gas-stream injectors is a typical requisite. The heattransfer efficiency (HTE) of in-furnace utilization of the heatso-generated is also relatively low, mainly because of the batch-wiseoperating mode, typical EAF or BOF geometric shape, and remoteness ofthe bath from the gas stream exit. Subsequent utilization, such as forpreheating scrap, has been only marginally viable as typically somewhatcomplex and costly to apply in practice. One object of the invention isto realize consistent and near-complete post-combustion includingefficient in-furnace heat transfer to the charge, as characterized byuniformly high PCD and HTE and also efficient utilization within theprocess system of the remaining sensible heat contained in the off-gasesfrom melting, thereby minimizing overall process energy requirements anddischarging into the atmosphere only substantially combustible-freeexhaust gases at low temperatures.

[0011] These current iron and steelinaking processes almost universallyfeature lancing or sub-surface injection of high-purity oxygen into thebath, typically at high pressures and high velocities in the sonicrange. The chemical combination of some of the oxygen with irongenerates iron oxide fume which is exhausted as fine particulates, withthe effect of reducing metal yields and polluting the environment.Another object of the present invention is to provide a steelmakingprocess which does not inherently involve injecting oxygen into thebath, using it only when needed for handling specific process materialsand special product requirements. A corollary object is to substantiallydecrease the generation of iron oxide fumes which are typical of currentcommercial steelmaking processes. Another corollary object is providingthe application for low-pressure oxygen of lower purity, such asgenerated from air separation by molecular sieves, instead ofhigh-purity, high-pressure oxygen.

[0012] Still another object of the invention is to release only aminimum volume of exhaust gases at relatively low temperature which aresubstantially free of combustibles, thereby carrying less heat lossesand pollutants into the atmosphere than other overall iron ore reductionand steelmaking combinations.

[0013] A further object is to accomplish transfer and immersion of hotsolid reduced iron from the reduction stage into a partially meltedmetal bath at the melting stage with minimum time, heat loss and contactwith the ambient atmosphere, furnace gases and steelmaking slag cover.

[0014] A still further object is to distribute the hot solid reducediron pieces at entry into the partially melted metal bath and dispersethem sufficiently to avoid the formation of agglomerated floatingislands of unmelted iron pieces and in-bath minimize slow mass transferas a barrier to fast heat transfer and melting.

[0015] Yet another object is to employ a minimum quantity of rawmaterials, additives, fuels, reductants and oxidants in a direct ironand steelmaking process, in which all of the principal process steps canbe conducted simultaneously and continuously to yield a continuousstream of liquid iron and steel having a controlled composition andtemperature.

[0016] As applied to foregoing Group A processes, the invention providesa process for direct iron and steelmaking which comprises introducingiron oxides containing pieces into a gas-solid reduction zone within areduction reactor fired by pressurized hot reducing gases comprisingrecirculated top gases enriched by externally reformed hydrocarbonsand/or directly introduced hydrocarbons and percolating said reducinggases through said gas-solid reduction zone for reaction with said ironoxides yielding hot solid reduced iron pieces, followed by transferringsaid reduced iron pieces into a gas-solid-liquid melting zone containinga partially melted metal bath carried within the inner side walls of anelongated rotary furnace having at least a partial top cover of floatingslag and fired by combustible and oxygen-containing gases generating agas stream of hot furnace gases passing above the bath surface supplyingheat for continually melting said hot reduced iron to yield liquid ironand steel, said gas stream exiting through an annular end opening ofsaid furnace, including the following steps, in combination: advancingsaid hot reduced iron along with any accompanying hot reducing gasesfrom within said gas-solid reduction zone into a transfer duct directlycommunicating between said reduction and melting zones and incorporatingan injection lance directed through an annular end opening of saidrotary furnace into said melting zone angled downwards towards said bathsurface; introducing pressurized carrier gases into said transfer ductentraining and propelling said hot solid reduced iron pieces throughsaid injection lance projecting a jet of said carrier gases and hotreduced iron pieces from said lance penetrating said metal bath surfacethereby submerging and dispersing said solid reduced iron pieces withinsaid partially melted metal bath; and dispersing said reduced ironpieces further within said metal bath following said submerging by meansof the propelling action of said inner side walls rotating against thebottom perimeter of said metal bath.

[0017] Sensible heat contained in the rotary furnace hot combustionproducts is preferably used as part of the preheat requirement of saidhot reducing gases. Externally reforming a minor portion of theenriching hydrocarbons by partial oxidation with oxygen is also apreferred feature, introducing the remaining major portion directly, asfollowed by in-situ reforming into reducing gases CO and H₂ within thegas-solid reduction zone.

[0018] When incorporating solid-state reduction under Group B, at ornear ambient atmospheric pressure, the invention includes an additionalstep of advancing the hot reduced iron into a pressurizing zone andapplying an elevated pressure therein by introduction of a pressurizinggas. Discrete particles of carbonaceous reductant, as coal char or thelike, when present mixed together with the hot reduced iron pieces, arepreferably removed by size-separation prior to iron pressurizing;transfer and injection, with the char subjected to cleaning andrecycling of this unreacted reductant material. The hot reducing gasesemitted from the melting zone are preferably transferred into thegas-solid reduction zone providing supplementary heat for iron oxidereduction.

[0019] As applied to both A and B, the principal process steps arepreferably and advantageously conducted continuously and simultaneouslywhilst the charge flows continually from charge to discharge. Theprocess of the invention includes introducing additionaloxygen-containing gases, such as by injecting at least 80 percent pureoxygen into the gas stream, which is directed to effectively realize (1)post-combustion of CO evolving out of the bath surface from combinationbetween carbon and oxygen as residual iron oxides contained in the hotreduced iron, and (2) reaction with any combustibles contained in thecarrier gases and accompanying hot reducing gases evolving from the jet,forming CO₂ and H₂O within the gas stream prior to said stream exitingthe melting zone, thereby supplying additional heat for melting. Inaddition to the distributing and dispersing effects of the solidsinjection lance stream impact area in combination with furnace wallrotation and slope, a preferred feature is distributing the area ofimpingement of the jet of carrier gases and hot reduced ironlongitudinally along the partially melted metal bath to facilitate themass and heat transfer requirements for most efficient melting, as bytraversing the jet alternately forwards and backwards within the meltingzone.

[0020] The process preferably includes advancing liquid metal into agas-liquid refining zone containing a completely melted metal bathcarried within the furnace and heated by a discharge end burnersupplying a portion of said combustibles and oxygen-containing gasesadapted to control the temperature of said melted metal bath essentiallyindependently of the heat requirements for melting within the meltingzone, agitating, homogenizing and refining the liquid metal under thecontrolled agitating action of the rotating furnace side walls to yieldliquid iron and steel of controlled temperature and composition. The gasstream of hot combustion products from the discharge end burner also cancomprise a substantial portion of the melting heat requirements. Thebalance of the heat for melting is supplied by post combustion andcombustion of gases evolving from the jet, which can be supplemented bya charge end burner firing directly into the melting zone.

[0021] Fluxes, alloys and carburizing agents to control and adjust thechemistry of the reactions in the gas-solid-liquid and gas-liquidreaction zones may also be introduced into said transfer duct forentrainment by said carrier gases and injection together with the hotreduced iron. Supplementary iron and steel scrap, pig iron, cold DRI orDRI briquettes may optionally be charged into the melting zone, as wellas provision for longitudinally traversing the point of introductionlongitudinally forwards and backwards.

[0022] Various other objects, features and advantages of the process andapparatus of this invention will become apparent from the followingdetailed description and claims, and by referring to the accompanyingdrawings in which:

[0023]FIG. 1 schematically illustrates features of the process andapparatus of this invention when applied incorporating reduction Group Aprocesses above, utilizing solid-state reduction within a progressivelydescending contact-supported bed within a shaft furnace reactor;

[0024]FIG. 2 is a section view along plane 2-2 of FIG. 1;

[0025]FIG. 3 is a graph of an exemplary longitudinal traverse cycle of alance adapted for injection of hot solid reduced iron into thegas-solid-liquid melting zone;

[0026]FIG. 4 is a schematic partial flowsheet incorporating reductionGroup A processes but within a fluidized bed reactor;

[0027]FIG. 5 is a schematic partial flowsheet incorporating reductionGroup B processes, as conducted in rotary kilns;.

[0028]FIG. 6 is a schematic partial flowsheet incorporating reductionGroup B processes, but as conducted on a rotary hearth;

[0029]FIG. 7 is a partial sectional side view illustration of a solidsinjection lance nozzle embodiment in operation, which is also adaptedfor oxygen injection into the gas stream;

[0030]FIG. 8 is a partial sectional side view illustration of a gasstream oxygen lance injection nozzle adapted to distribute oxygen forpost combustion across the gas stream;

[0031]FIG. 9 illustrates an alternative embodiment of a nozzle as inFIG. 8;

[0032]FIG. 10 is a schematic of an alternative partial flowsheetincorporating reduction Group B processes, as conducted in rotary kilns;and

[0033]FIG. 11 is a sectional side view illustrating features of aneductor assembly as in FIG. 10 for accelerating the hot reduced ironpieces for injection.

[0034] Referring to the flowsheet FIG. 1, a gas-solid reduction zone 1is maintained within a reduction reactor 2. A charge of iron oxidescontaining pieces 3, generally as lumps or pellets, are fed via at leastone reactor feed inlet 4 to comprise a contact-supported bedprogressively descending by gravity, through the interstices of whichpressurized hot reducing gases 5 introduced via inlets 6 percolateupwards through zone 1, countercurrent to the general movement of thesolid charge, reacting with the iron oxides to yield hot reduced iron58. The reacted top gases 7 exit via outlet 8 leading into cyclone 9 forremoval of particulates and on to cooler-scrubber 10 effecting removalof H₂0 prior to repressurizing by recirculating compressor-blower 11.

[0035] At the same time, a gas-solid-liquid melting zone 12 containing apartially melted metal bath 32 is maintained within rotary furnace 15wherein hot charge material discharged from zone 1 is melted. Zone 12 isoptionally followed by a gas-liquid refining zone 18 where chargecomposition and temperature are adjusted and stabilized prior todischarge. The zone(s) are fired with combustible and oxygen-containinggases introduced, as required, by a charge-end burner 19 and adischarge-end burner 20. The gas stream of hot combustion products passcounter-current to the general charge movement exiting via annularcharge end opening 21 into an exhaust duct system which may include agas-conditioning chamber 22 for removing particulates and apressure-control damper 23. The hot gases 33 then supply heat input forrecirculated top gas heater-recuperator 24. Discharge of liquid metal 25can be via a tap hole 26 into a ladle 27, or via a siphon tube 28 into avacuum vessel 29 which, as well as lockhopper 30 for alloying,deoxidation and fluxing additions, may incorporate features for gasbubbling, oxygen injection, heating and the like, prior to discharge,for example, into a launder or tundish 31 for feeding a casting machine.

[0036] In the embodiment illustrated, the reacted, dewatered andpressurized top gases 35 are divided into three gas streams. The firststream 36 is utilized as fuel 42, 43 for burners 19 and 20, as alsosupplied with oxygen 44 & 45. A second stream 37 is combusted with airor oxygen in direct-fired heater 40 to yield heated gases 41 which,together with hot combustion product gases 33, make up the total heatinput for heater-recuperator 24. The exhaust gases 73 then pass via acooling chamber 74, preferably using water spray-mist, through exhauster75, damper 76, dust collector 77 into the atmosphere via stack 78.Cooled, cleaned waste gases 79 thus appear as the only waste gasesemitted by this flowsheet, which are substantially free of combustiblesand particulates. The third and major stream 38, after passage throughheater-recuperator 24, furnishes hot recirculated top gases 50 ready forenrichment, temperature adjustment and recirulation into zone 1.

[0037] As illustrated, hydrocarbons 51 are introduced into mixingchamber 52 as reducing gas makeup. Hydrocarbons 51 B may optionally beintroduced directly as an unmixed component of reducing gases 5. When inthe form of fuel oil, hydrocarbons 51, 53 are suitably atomized, forwhich a minor portion of pressurized top gases 35 can be applied as theatomizing medium. In order to balance the energy and oxygen requirementsof the flowsheet illustrated, hydrocarbons 53, suitably about one-thirdof the total makeup, are partially combusted with oxygen 54 in a gasgenerator 55, yielding hot reducing gas 56 predominantly comprising COand H₂. Pressurized hot reducing gases 5 thus comprise a mixture of hotrecirculated top gases 50, fresh hydrocarbons 51, 51B, and partiallyoxidized components 56 of hydrocarbons 53.

[0038] Numerous solid-state reduction process variations are availablederived from known processes. For example, a flowsheet could includeprior reforming of all of the makeup hydrocarbons, either beforeintroduction into the top gas recirculation circuit (HYL), or combinedwith it (MIDREX). It could include steam as a reformer (HYL) or air as apartial oxidation agent (AREX). It could include removal ofrecirculating CO₂, such as by hot potassium carbonate scrubbing(PUROFER) or mono-ethanol-amine absorption (NIPPON STEEL & IRONCARBIDE), or PSA absorption (HYL). Reduction zone 1 can also be operatedat various pressures from about 1 atmosphere to more than 5 atmospheres,significantly increasing production rate as pressure increases (NIPPONSTEEL). Appropriate adjustments are involved in each case to meetoperating ranges for material balance of C, H and O in combination withenergy balance for satisfactory reduction temperatures.

[0039] Whilst a large number of different reducing gas recirculationcircuits thus are feasible, this particular one is considered uniquelyadvantageous because the extra oxygen required as makeup, in addition tothat supplied by the iron oxides, is met without introducing diluentnitrogen to slow down the gas-solid reduction reactions and absorb heatfor reheating each time around the circuit, at the same time supplying asubstantial part of the makeup heat requirement by direct reaction inthe partial reformer, avoiding additional energy losses characteristicof indirect heat exchangers and external reformers. Also, a substantialpart of the makeup hydrocarbon gas is already reacted into CO and H₂preceding reactor entry, thereby being ready for immediate iron oxidereduction and reducing the amount of temperature loss by the endothermiccracking of hydrocarbons within the gas-solid reduction zone. Theseadvantages are immediately evident from a material and energy balancecomparison with reduction process prior art.

[0040] Hot reduced iron 58 confined together with pressurized hotreducing gases at the bottom of reactor 2 is maintained ready fortransfer on to the gas-solid-liquid melting zone 12. A rotary valve 60,enclosed screw or other known mechanical device can be used to controlthe iron transfer rate through conduit 61 connecting into transfer duct62 which connects into injection lance 63, adapted for projecting thehot reduced iron through opening 21 into partially melted bath 32 withingas-solid-liquid melting zone 12. In normal operating mode the hotreduced iron 58, along with hot reducing gases leaked from zone 1through valve 60, pass into transfer duct 62. Pressurized hot carriergas 65, drawn as a minor part from the recirculated pressurized hot topgases 50 in the embodiment illustrated, is introduced into transfer duct62 within which it combines with the solid reduced iron and anyaccompanying reducing gases introduced from conduit 61 entraining andpropelling the hot reduced iron through injection lance 63 incorporatinga lance nozzle 34 angled downwards and directed towards the surface ofbath 32 projecting a jet 64 into partially melted metal bath 32.Regulation of the gas flow rate by means of control valve 66 thencontrols the gas flow and velocity of jet 64, and thereby the depth ofpenetration of the hot gases and reduced iron pieces into bath 32 uponimpingement with the bath surface. Additives 16, such as fluxes andalloys and carburizers, may be injected together with the hot iron, suchas introduced from pressurized additive feed hoppers 17, also connectinginto transfer duct 62 and utilizing feed rate controls according toknown pneumatic feeding and conveying practice.

[0041] The density of pieces of hot reduced iron is typically in therange of 2.0-3.8 g/cc, as compared to slags of 3.1-3.5 g/cc and metalbath in area of 7 g/cc. Initially, then, the tendency is for the solidreduced iron pieces to rise after impact and float on the metal with topcaps projecting somewhat above the bath surface into the slag layer.Also, when a piece or pellet of reduced iron is immersed in a liquidiron bath, a solid shell or surface crust of frozen melt typically formsinitially on the pellet surface before remelting this crust and meltingthe pellet on to complete dissolution. Melting occurs by a combinationof heat and mass transfer and the subject system, when operating withlance nozzle 34 stationary, concentrates a relatively large mass flowrate of unmelted material into the impact area of jet 64. For example,if hot reduced iron 58 is being generated at the rate of 60 tons perhour, as typical of a modest-sized shaft furnace reduction, about 33pounds of iron per second is propelled into bath 32. Lacking a positivemechanism dispersing the unmelted iron pieces, they can remainconcentrated in the bath area around the impacting jet, even possiblyagglomerating and creating floating islands of predominantly still solidreduced iron pieces. Referring to FIG. 2, it is seen that the inventionprovides such a dispersing mechanism by the propelling action of theinner side walls of furnace 15 rotating against the bottom perimeter ofbath 32, acting in combination with the dispersing force of the piecevelocity in jet 64. The dispersing effect can be increased by increasingfurnace rotating speed, even up to ten or more revolutions per minute.Increasing the angle of furnace incline also increases the longitudinalcomponent of the dispersing movement.

[0042] As the rotary furnace size and also the ratio of length todiameter within the zone 12 refractory walls is increased, it isincreasingly difficult to spread the melting heat requirements similarlyto the heat release availability from the hot furnace gas stream andrefractory walls throughout melting zone 12 by relying mainly on jetvelocity, furnace rotation and sloping for dispersion of unmelted ironpieces. One option is to employ additional solids injection nozzles orlances spread at intervals along zone 12. As another option and apreferred feature of the invention in the embodiment illustrated, lance64 is adapted to provide variable positioning and traversing of nozzle34 within melting zone 12, forwards and backwards in the longitudinaldirection.

[0043] Cantilevered lance 63, as supplied with hot reduced iron viatransfer duct 62 incorporating flexible hose section 90, is carriedbetween a fixed troughed supporting guide roller 48 andretractable/releasable pinch idler roller 49, with lance entry endclamped onto moving carriage 47 incorporating support guide rollersrunning on a longitudinal guide track 39. Traversing and/or setting thedistance of insertion of nozzle 34 into melting zone 12, for example,can be accomplished by a reversible variable speed hydraulic or electricmotor driving roller 48, having end travel and intermediate positioningpoints based on limit proximity switches along track 39 sensing theposition of carriage 47. Vertical adjustment can optionally be included,such as by cylinder 59 vertically rotating track 39 about a pivot 57.The lance access opening through charge hood 46 is appropriately sealed,at least partially, such as by an annular gas curtain and is preferablyelongated as a vertical elongation covered by a removable panel or doorduring operation, to allow clear passage of angled nozzle 34 duringlance insertion or removal for maintenance and the like. Exampleapparatus variations would include substitution of linear bushings inplace of roller assembly 48, 49 and carriage 47, and traversingactuation by means of ball screws or a longitudinal hydraulic cylinder.

[0044] The hot reduced iron can be longitudinally distributed bycontinuously traversing lance nozzle 34 between a maximum insertedlength Lmax and minimum inserted length Lmin. For example, graph FIG. 3illustrates a cycle in which the nozzle traverses backward from positionLmax at a uniform speed of 1 ft./second until it reaches Lmin, where itreverses and returns to Lmax at 3 ft./sec, when the cycle is repeated.Increasing the speed of nozzle travel in one direction relative to theother, as in the illustration, is perhaps the simplest method ofminimizing the effects of sudden and cyclical “double dosing” adjacentto the reversing points. In order to meet preferences for concentratingthe solids in a particular area., the lance travel speed pattern can, ofcourse, be changed in steps, or accelerated and decelerated according tothe pattern desired. A principal consideration in selecting the Lmaxposition is the completion of melting prior to molten iron exit from themelting zone 12. An Lmin setting close to charge end opening 21 assistswith full use of available heat transfer areas, avoids unnecessarylocalized superheating of bath 32 at the charge end and reduces thetemperature of hot gases 33. Conversely, at small Lmin, there may beinsufficient time for reaction of combustibles contained in the carriergases to form CO₂ and H₂O prior to their exit from opening 21. A gassampling and analysis system continuously monitoring the combustible andoxygen content of gases 33 can appropriately assist with selecting themost suitable Lmin distance. The distance Lmax-Lmin would preferably beat least half the total length of zone 12, usually in the range 70 to 90per cent.

[0045] As seen in FIG. 2, the moving furnace walls cause a generalmovement of metal proximate the bath bottom in the direction of wallrotation, which results in a compensating movement in the oppositedirection near the bath surface, shifting unmelted charge laterally awayfrom the lance path during the time interval between the two passes ofeach cycle. Locating the lance path on the upstream side of the lateralmetal movement near the surface, as illustrated, tends to distribute theunmelted iron across the width of the bath throughout the operatingperiod.

[0046] As illustrated, nozzle 34 is angled downwardly at an angle ofapproximately 45 degrees and pointed towards the discharge end offurnace 15, but could be any suitable acute angle up to 90°,perpendicular to the bath surface. Steep angles increase jet penetrationdepth and shallow angles favor more turbulent mixing of spent carriergases with furnace gases and oxygen, and longer in-furnace time,therefore more heat transfer and complete combustion of containedcombustibles prior to their exit from opening 21.

[0047] In the embodiment illustrated in FIG. 1, conduit 61 incorporatesa diverter valve 67 adapted to divert hot reduced iron 58 via alternateconduit 68 into a water quenching 69, dewatering 70 and drying 71process sequence to yield cold direct reduced iron 72 as an intermediatealternative product. Also included is capture and recycling of hotreducing gases leaked through valves 60, 67, such as by venting conduit68 and piping the gases to the inlet of blower 11. It is to be notedthat shaft furnace infeed pellets or lump ore are typically sized to belarger than 3 mm and the reduced iron 58 is similar, except for theaddition of minor quantities of fines by in-process degradation. Sincethe ratio of wetted surface area to weight is correspondingly low, thenby limiting the moisture pick-up during quenching essentially to surfacewetting only, only a minor quantity of moisture is picked up. Bylimiting quenching time to discharge the wetted pellets at elevatedtemperature, usually somewhat above 100 C, they are essentiallyself-drying during cooling, yielding a cooled dry reduced ironintermediate product. without a requirement for external drying heat.This cold direct-reduced iron can be re-introduced as another additivefor melting, such as via pressurized hoppers 17, thereby avoiding anyyield loss of liquid iron and steel. Another advantage of quenching isthe opportunity to add a passivating coating agent dissolved orsuspended in the quench water to minimize reoxidation during storage orshipment of cold DRI pellets, thereby eliminating necessity for asubsequent passivating step by spraying or the like.

[0048]FIG. 4 illustrates a flowsheet with Group A solid-state reduction,but with fluidized rather than gravity contact-supported beds. Afluidized bed 80 is confined in a gas-solid reduction zone 1 within areactor 81 fed with iron oxides containing pieces 82 which are fluidizedby pressurized hot reducing gases 5. The illustration is veryabbreviated, omitting various features and variations which would beevident from the numerous known and applicable fluidized bed iron orereduction process technologies. These generally process smaller ironoxides containing pieces less than 3mm and employing bubbling andrecirculating fluidized beds in various flowsheets and mechanicalconfigurations. Top gases 83 generally carry heavy loadings of chargeand, like the shaft furnace processes, a major portion of cleaned topgases 84 is usually dewatered, pressurized, heated, enriched andrecirculated, after separating out most of the charge particles 85 incyclone 86 and returning them to fluidized bed 80. The hot solid reducediron 87, which can range from low-carbon metallic iron throughcarburized iron to nearly pure iron carbide Fe₃C plus free carbon,similarly passes through a conduit 88 at a rate regulated by flow ratecontrol valve 89 into transfer duct 62 where it is picked up bypressurized carrier gas 65 for injection into gas-solid-liquid meltingzone 12 via an injection lance 63, in ajet 64 emitted from nozzle 34.The lance traversing features in FIG. 1 are not illustrated, as benefitsmay be marginal in some circumstances, such as when supplementarymetallic charge materials 13 in the form of iron and steel scrap, HBIbriquettes, or the like are fed into zone 12 by other means, such as byan oscillating feed conveyor 14, to comprise a substantial portion ofthe charge into melting zone 12. As illustrated, feed conveyor 14 mayride on wheels running on a track longitudinally aligned with furnace15, and adapted to provide forwards and backwards traversing of theconveyor and thereby longitudinal distribution of the entry position ofcharge materials 13, which are then further advanced and dispersedwithin bath 32 by the action of the rotating inner furnace walls incombination with downward slope of furnace 15. Fluxing and alloyingmaterials, or cold reduced iron pellets as additives 16 may also be fedfrom pressurized hoppers 17. Incorporating a flexible hose section 90into transfer duct 62, both typically comprising heat resisting alloyand externally insulated, facilitates locating reactors 2 or 80 at anydesired level or location relative to furnace 15 and also adjustment ofthe insertion distance and angle of injection pipe 63 into zone 12, evenwhen not required for lance traversing. Facilitating the sealing ofcharge hood 46 when mounted to float with the movement of rotary furnace15 is another advantage, particularly if injection pipe 63 is directlysupported by charge hood 46.

[0049] Provision for diversion, cooling and discharge of the hot reducediron, analogous to FIG. 1, of course, can be included, but naturallyrequires more extensive dewatering and drying measures because of themuch smaller piece sizes or, alternatively, indirect cooling without anydirect water quenching may be applied, as well known in the art ofdirect reduction. Also analogous to FIG. 1, hot gases 33 are routed to aheater-recuperator which preheats fluidizing reducing gases 5. A typicalfluidized bed iron carbide reduction circuit, for example, employs anexternally fired supplementary heater for preheating to the 1200° F.area, as replaceable by utilizing heat contained in gases 33.

[0050]FIG. 5 illustrates a flowsheet in which the solid-state reductionis a Group B process with gas-solid reduction is carried out within anelongated moving bed 93 which is continually advancing by rotation of aslightly down-sloping rotary kiln reactor 94. Charge components,typically comprising iron oxide containing pellets or lumps, coal, coalchar and limestone or dolomite as a sulphur-adsorbent are fed from bins117 by means of controlled rate feeders into reactor 94 via a commonconveyor or charge chute 118. The reductant for most rotary kilnreduction technologies is coal or char intermixed with the iron oxide asseparate discrete particles which, upon heating, react to form reducinggases CO and H₂ within bed 93 yielding a reacted mixture 97 comprisingpieces of hot solid reduced iron, coal char, residual ash andsulphur-adsorbent fluxes. The coal/coal char also furnishes a major partof the total heat requirement, air or oxygen being introduced throughports or burner pipes 96 at intervals along reactor 94, or discharge endburner 119, which may be supplemented with liquid or gaseous fuel, ifrequired to maintain the desired reaction temperature profile. Asdiscrete pieces, the coal and fluxes of charge mixture 92 canconveniently be sized smaller than the iron oxides containing pellets orlumps, facilitating a separation by means of enclosed hot screen deck 98usually at about 6 mm, to yield a continual flow of substantially cleanhot reduced iron 99 as oversize pieces ready for direct transfer tomelting zone 12. The screen deck 98 typically is vibrated and the screenbars may be internally water-cooled and/or comprise heat resisting alloyconstruction. The screening optionally can also include a top deck (notillustrated) with openings sized appropriately for scalping off anylarge chunks of agglomerated charge, directing them into an appropriateclosed hopper including a gate for periodic discharge.

[0051] As well as components of charge mixture 92, coal and char can beintroduced along bed 93, such as by pneumatic injection which is commonpractice in the art of iron reduction in rotary kiln reactors. Gas flowis generally countercurrent to the bed movement within gas-solidreaction zone 95, exhaust gases 135 exiting the charge end opening viacharge hood 136 into an appropriate cleaning and discharge system,optionally including recuperation of sensible heat.

[0052] The hot reduced iron 99 may be discharged through a chute andsurge hopper 100 submerging the inlet of a rotary valve 91, oralternative such as a screw or gate-lock feeder, discharging thematerial into transfer duct 62 for entrainment by carrier gas 101,projecting the reduced iron through duct 62 to lance 63. The rotaryvalve 91 would typically be of the offset type, preferably includingother special features known in the art of rotary airlock valves whenfeeding relatively hot and large-sized pieces in pneumatic conveyingsystems. Since, unlike Group A where gas-solid reduction zone pressuresare typically higher than 1 bar, Group B solid-state reduction processescharacteristically are controlled to a set point typically within ±3 mmwater column of ambient atmospheric pressure, leakage and backflow ofcarrier gas through valve 91 can represent a significant quantity ofgas. Optionally, a major portion of this gas can be vented to atmosphereor vented to the carrier gas pressurizing circuit for recycling.

[0053] Pressurized carrier gas 101 is most conveniently supplied from anexternal source, since hot pressurized recirculating gases are notinherently available from the process flow. Other alternatives includepressurizing a portion of gas-solid reduction zone exhaust gases 135, orinserting a carrier-gas inlet duct into the gas-solid reaction zonethrough hood 115, then pressurizing the kiln gases using ahigh-temperature blower, to comprise carrier gas 101. As thesereduction-zone gases are hot, with composition usually reducing orneutral towards hot reduced iron, reoxidation and temperature lossduring transfer are minimized with this option. The hot combustionproduct gases 112 exiting gas-solid-liquid reaction zone 12,characteristically in the area of 1600 C and containing only minorquantities of unburned CO, H₂ and hydrocarbons, can be transferred viaexhaust transfer duct 114 into gas-solid reaction zone 95 to furnishpart of the heat requirement therein. Note that stationary enclosedheads 115, 46 which are preferably sealed at the junctures with therotary furnaces, also incorporate the various items of transferequipment. Duct 114 may also include a by-pass, such as for exhaustdischarge when reactor 94 is not operating and alternatively, exhaustgases 112 may be utilized for air, oxygen or fuel gas preheating or foroxide pellet preheating, etc. The near-complete reaction of combustiblesto CO₂ and H₂O within zone 12 is typically less important for Group Bthan Group A, as there is a second opportunity in the gas-solidreduction zone for these gases to complete in-process combustion,whereas in Group A they are typically utilized only for recuperation byindirect heat transfer.

[0054] The hot screening undersize suitably discharges into a quench120, followed by wet magnetic separation 121 to recover the iron 122 forrecycling, for example, on to fine grinding 123, dewatering bythickening 124 and filtering 125, for addition as a component of themixture for iron oxides balling and pelletizing. This iron 122, 126could also be applied as a melting additive 16, 17. The non-magnetics126 may be wet-screened 127 to pass the undersized fine ash and hydratedsulphur-adsorbent 128 to a waste settling pond. The oversized coal char129 can be dewatered and then recycled to comprise a portion of thesolid carbonaceous reductant in bed 93. Known solid-state rotary kilnreduction has also been applied to reduction of iron ores andconcentrates which are balled, such as by a disk or drum pelletizer, andcharged in the moist green, pre-dried, dried and preheated condition, orpre-hardened by a low-temperature curing process, without priorinduration by heating at high temperature. In such a case, recycled coalchar, after appropriate comminution, can be mixed with the concentrateprior to balling to comprise a constituent of the pellets for reduction,thereby also comprising a component of the solid carbonaceous reductant.Fresh carbonaceous material can also be added to such pellets, wherebythe combined recycled and fresh carbonaceous material contained in thepellets may comprise a substantial portion, or even all of, the solidcarbonaceous reductant employed in the gas-solid reduction zone. At highlevels of contained carbon in the pellet charge materials, screening 130and the recycling circuit 121-129 becomes largely superfluous. Theentire reacted mixture 97 can also be by-passed to quench 120, such asby rotating a hinged screen bar entry section 130, followed by wet coldscreening 127, with the oversize 131 being directed to drying 132 toyield cold direct reduced iron pellets 133 which can be introduced intozone 12 either directly or injected as another additive 16, 17. Wetscreen undersize 134 may rejoin the fine-sized material cycle justdescribed.

[0055]FIG. 6 illustrates Group B gas-solid reduction in which a charge138 comprising formed pellets of mixed fine-sized iron oxides containingpieces and coal is distributed as a thin layer upon a rotating hearthwithin rotary hearth furnace reactor 139. Heating fuel 140 is typicallyintroduced via burners at intervals along the hearth and preheatedcombustion air 137 from blower 144 is also distributed to control chargetemperature profile and complete the combustion of the hearth gases.Interior gas flow is countercurrent to the hearth rotation and exhaustgases 141 exit close to, or coincident with, the feed of charge 138.Rotary furnace combustion product gases 112, are appropriately channeledinto furnace 139 providing supplementary heating. Gases 141 typicallypass through a conditioner 145, heat recuperator 146, dust collector147, exhauster 148 and stack 149. Since the solid reductant is aconstituent of the pellets, they can be passed directly into the hottransfer and injection system without screening. Illustrated is analternative system applicable to higher transfer pressures, also withoutcarrier gas backflow, as particularly applicable for transferring thehot reduced iron over long distances preceding injection. The hotreduced iron is passed through a closed chute into surge buffer hopper100, which intermittently discharges into hopper 102, as alternativelypressurized for transfer into continuously pressurized hopper 103 anddepressurized to receive hot reduced iron from hopper 100. The systemincorporates suitable isolating and control valve means, such as solidsflow control valves 104, 106 and sealing valves 105, 107. Hopperpressures optimally can be controlled by a regulator 110 on branchcarrier gas line 109, also including a shut-off valve 111 having closuresynchronized with opening of valve 105. Surges of reduced iron fromhopper 103 into transfer duct 62 may be evened out, such as by a rotaryor a metering valve 108. Alternatively, a two-position gate can beemployed at 107, alternately diverting hot reduced iron directly intoeither of two pressurized hoppers 103 feeding into transfer duct 62 inparallel. Numerous equipment and control alternatives are thusavailable, according to the art of pneumatic conveying.

[0056] The hot reduced pellets 142 characteristically contain residualcoal char and coal ash, which result in significantly greater slagvolumes in zones 12, 18 and higher feed rates of fluxing additives forsimilar slag basicity ratios. In this case, a method for continuouscontrolled slag discharge, separate from and simultaneously with theliquid iron and steel is particularly advantageous, such as described inmy U.S. Pat. No. 5,305,990. Also illustrated is a variation of lance 63with a straight in-line nozzle 34 and pivot 57 placed closely to opening21 and approximately intersecting the lance center line, thereby beingadapted to allow longitudinal traversing of jet 64 also by rotation oflance 63 about pivot 57, as well as by longitudinal traversing of lancecarriage 47. Flattening angles of impingement with the bath surface withincreasing distance of insertion is a possible disadvantage of thisarrangement.

[0057] In another variation of solid-state reduction on a rotatinghearth (COMET), alternate layers of fine-sized iron oxides containingpieces and a coal/limestone mixture are heated for reduction coincidentwith weak agglomeration of the iron fines, whereby a hot size-separationstep as in FIG. 5, preferably followed by a lump-breaking step appliedto the iron oversize, yields a continuous flow of hot reduced ironadaptable for transfer and injection.

[0058] Pressurized air, preferably preheated, is an obvious option as acarrier gas. Since oxygen is oxidizing to iron but also tends to oxidizecarbon in preference to iron at typical hot reduced iron temperatures anabove, reoxidation of iron would be minimal during the brief period fortransfer and entry, also considering that the iron pieces, particularlywhen in Group A, generally carry a surface layer of finely dividedcarbon as soot particles or the like. Disadvantages are dissolution ofnitrogen in the melt which is potentially very detrimental to productquality, along with some premature and unpredictably variableconsumption of carbon which otherwise would be useful for reduction ofFeO. Inert carrier gases such as argon are easily applied, to bebalanced against relatively high cost and the fact that they wouldsimply dilute gas-solid-liquid melting zone gas stream withnon-radiating gases (versus CO₂ and H₂O as strong radiators), therebydecreasing effective heat available. Carrier gases may be preheated, oralso introduced cold at the temperature of available supply. Consideringrelative specific heats, heat and mass transfer, cooling hot reducediron during transfer by carrier gases at ambient temperature generallywould be less than 15 per cent, that is, when carrier gas volumes are onthe usual order of 4 moles per ton of iron transferred. To this lossmust be added the cooling effect on the heat balance for zone 12.

[0059] Hot direct reduced iron typically contains carbon in the rangefrom about 1 to 2 per cent, or 20 to 40 pounds per ton, and oxygen from1 to 3 per cent combined nominally as wustite, FeO, both of which aredispersed throughout the hot reduced iron pieces. Upon introduction andmelting in metal bath 32, a carbon boil therefore proceeds as expressedby the reaction FeO+C=CO+Fe, requiring heat input of about 80,000 btuper ton of iron for each 1 per cent carbon, and also evolving 600 cubicfeet of mainly CO gas from the bath and slag surface into the gasstream. By near-complete post combustion of this CO therein at furnacetemperature by reaction with oxygen at near-ambient temperatureaccording to the exothermic reaction CO+½O₂=CO₂, about 180,000 btu perton can be released into the gas stream prior to exit from opening 21,considering the CO at 2800 F. bath temperature and the oxygen at ambienttemperature. This heat is then available to assist in melting by heattransfer to the metal and slag, and also as residual sensible heat foruse in the gas-solid reduction stage. Since there is also a propensityfor oxidation of additional iron to form additional FeO in the metalbath and slag, these conditions typically require only supplementarycarbon, such as a component of additives 16, in order to meet the carboncontent range of most commercial steels in the product metal. To providea perspective on the relative quantities of heat, the sensible heatcontent of a steel melt at 2800 F. is approximately 1,200,000 btu pershort ton.

[0060] The additional oxygen is thus employed mainly for two separate,if related, purposes: (1) post-combustion of CO evolving from a carbonboil within bath 32; and (2) combustion of carrier gases and anyaccompanying hot reducing gases evolving from jet 64. For purpose (2),the combustible gases to be reacted are essentially concentrated near tothe jet 64 impingement location, whereas for purpose (1), they are moreuniformly distributed across the surface area of bath 32. Should thetotal additional oxygen be directed into the area of jet 64accomplishing purpose (2), transfer and mixing with the general gasstream may be inadequate for purpose (1), therefore a portion or all ofthis post-combustion oxygen may be supplied by separate gas-streaminjection, or as excess oxygen with the fuel via burners 19, 20, or acombination.

[0061] The volume of carrier gases and accompanying reducing gasesleaked from the gas-solid reduction zone via conduit 61 may varyconsiderable according to the distance and difference in elevationsbetween the reduction and melting zones, but would usually be between 2and 8 pound-moles per ton, typically 4 pound-moles or 1500 standardcubic feet. Typically, only a minor portion of these gases reacts withthe melt and the major portion evolves into the gas stream around jet64. The heat potentially releasable by reaction with oxygen depends uponthe combustible content, amounting to about 270,240 and 780 btu percubic foot of contained CO, H₂ and CH₄ respectively, which is containedin jet 64 at 1500° F. for example, reacting to form CO₂ and H₂O at 3300°F. This heat would be zero or close to zero in some circumstances, suchas Group B process employing air, CO₂ or inert gases as pressurizing andcarrier gases.

[0062] When the bath C and O are approximately stoichiometricallybalanced in the melt, or there is a carbon deficiency, the process doesnot inherently require oxygen injection into the bath. Any additionalcarbon required to meet the desired liquid iron or steel carbon contentcan be injected as an additive 16 or introduced by other means. Thetotal quantity required also reflects additional FeO usually formed bymetal and slag oxidation within the melting and refining zones. Optionsinclude alternative deoxidizers such as manganese, silicon, calcium,aluminum and special mixes for reacting with part of the FeO, creatingreaction products which report in the slag rather than the hot gasstream.

[0063] Certain operating practices under Group A and rotary kilnreduction processes under Group B can obtain as low as 0.1 per cent C inthe reduced iron, or only two pounds per ton. In such a case,substantial additions of carbon or other deoxidizers can be involved toavoid over-oxidation of the melt and maintain the desired carbon levelin the melted product. Conversely, if the carbon level in the hotreduced iron substantially exceeds the stoichiometric amount forreaction with FeO, then bath oxygen injection is the obvious option. Aprincipal difference is a bath heat release of about 40,000 btu per tonfor each 1 per cent (20 lb.) of carbon oxidized to CO, rather than80,000 btu absorbed. Any oxygen contained in carrier gases may beconsidered essentially equivalent to such separately injected oxygen.

[0064] An iron carbide reduction process combination is pertinent forillustration, since the hot reduced iron pieces typically contain bothhigh carbon and high oxygen as iron oxides. As an example, assume thatthe iron carbide contains 5 per cent carbon and 6.5 per cent oxygen,with 0.5 per cent carbon desired in the melted product. To simplify theillustration, also assume any FeO formed by in-furnace iron oxidation isreacted with other deoxidizers. If 0.5 per cent by weight of the oxygenreports as FeO in the slag, then 4.5 per cent carbon stoichiometricallybalances the remaining 6 per cent oxygen for the reaction C+FeO=Fe+CO,leaving 0.5 per cent carbon remaining in the melt. The volume of COgenerated by this carbon boil would be about 4.5 (600)=2700 standardcubic feet and the heat absorbed 4.5 (80,000)=360,000 btu per ton.Post-combustion with approximately 1350 cubic feet of gas streaminjected oxygen is required for reaction of the CO forming CO₂,accompanied by a heat release of about 4.5 (180,000)=810,000 btu per tonof steel melted. Since the heat in the gas stream is then also utilizedin the reduction zone circuit, high heat transfer efficiency (HTE) ofthis heat into the melt is beneficial but not critical to the overallheat efficiency of the process. The HTE however, is substantially higheranyway than in an EAF or BOF with post-combustion because of theelongated melting zone shape and rotating furnace walls also agitatingand transferring heat into the bath, and the continuous, essentiallysteady-state operation. Low-oxygen as an objective in the art of ironcarbide reduction markedly reduces the production rate attainable,whereby designing the melting zone process operation to handle highoxygen enables much higher production rates to be obtained from similarreduction-stage equipment, reflected in lower capital costs.

[0065] Group A processes characteristically have pressurized andpreheated recirculating top gases 50 containing combustibles CO and H₂readily available for use as carrier gases, and also the hot reducinggases 5 enriched with fresh hydrocarbons. These gases can be suitableand potentially advantageous, particularly if their combustion withinzone 12 is controlled to take place mainly near the location of highestprocess heat requirements and proceeds substantially to completionin-process, at the same time avoiding exhaustion of unburnedcombustibles into the atmosphere. Hydrogen can dissolve in the melt upto the equilibrium value with molten iron at the partial pressure of H₂present in the carrier gas, that is, usually in the range 8-16 parts permillion corresponding to 25-50 per cent H₂ in the carrier gas, asgoverned by known thermodynamics of iron and steelmaking. At leastpartial removal is effected by the carbon boil action, as well as anysubsequent vacuum stage such as in vacuum vessel 29, but any possiblenegative product quality effect should be evaluated for the particularprocess and end product involved.

[0066]FIG. 7 illustrates a solids injection lance embodiment alsoadapted to introduce gas-stream injected oxygen for quick mixing andreaction in zone 12 with combustibles contained in carrier gases. Nozzle34 from lance 63 is directed downward at an acute angle to the surfaceof the liquid metal bath, which is about 45 degrees as illustrated, andthe jet 64 of carrier gases, hot reduced iron and additives separatesthe slag layer 152 and penetrates into bath 32 creating a turbulentcavity 157. Nozzle 34 carries an oxygen injection annulus 153 and iscooled by a water jacket 155 according to known lancing practices.Oxygen jet 156 may be emitted from an annular or semi-annular slit 154as illustrated, or from an individual nozzle or plurality of nozzles 159(see FIG. 2), preferably at relatively low pressure and velocity sincemetal or slag penetration is not sought, but rather interception andreaction with spent carrier gases and any accompanying hot reducinggases 158 as they evolve and rise above the bath, following dissipationof jet 64 kinetic energy, and carrier gas emergence from cavity 157.Accordingly, mixing and combustion between carrier-gas combustibles andoxygen, with consequent heat release, mainly takes place immediatelyabove the bath area containing the greatest concentration of unmeltediron. Oxygen delivered by nozzle such as 154 could, or course,alternatively be delivered by means of a separate oxygen lance to thatof lance 63.

[0067]FIG. 8 illustrates a gas stream oxygen injection lance nozzle 160particularly adapted to intercept and mix the oxygen with the generalgas stream flow 151, favoring purpose (1) post-combustion of the COevolving from a carbon boil within the bath. Oxygen is introduced viaannulus 161 between water-cooled cylindrical outer pipe 162 andwater-cooled inner pipe 163 carrying an oxygen jet flow rate, directionand distribution control disc 164. Annular slit nozzle opening 165 isthereby defined between the end of outer pipe 162 and the back face ofdisc 164, through which oxygen jet 166 fans radially outwards in acontinuous curtain of oxygen transversely spanning across the axiallyflowing gas stream. Disc 164 is preferably water-cooled, such as bycooling water supplied by internal water pipe 168 and returned via innerpipe annulus 169. Opening 165 can be shaped to enhance effectiveness ofmixing with the gas stream to increase reaction with combustibles. Forexample, in the illustration, slit opening 165 is angled upstream atabout 30° to the perpendicular, emitting a cone-shaped curtain radiallyoutwards which is also countercurrent to the general gas stream flow.Also, the sector of opening 165 directing oxygen jet 166 downwardstowards bath 32 is made wider than the sector directing the jet upwards,thereby delivering a higher volume of oxygen to directly intercept theCO evolving from the bath surface. The width of opening 165 and therebythe oxygen flow rate at a selected pressure and velocity, can be variedby axial location adjustment of pipe 163 by axial sliding of inner pipelocating guide 167 to different locations within outer pipe 162, forexample, by applying different thicknesses of spacer washers against anentry-end flange of inner pipe 163. FIG. 9 illustrates a gas streamoxygen lance injection nozzle embodiment variation, in which asimilarly-mounted disc acts only as a deflector disc 170, adapted todeflect oxygen jet 171 outwards projecting an annular oxygen curtainacross the furnace gas stream cross-section.

[0068] Such gas stream oxygen injection provides for the post-combustionoxygen intersecting the bath surface transversely to the direction ofmetal flow, as well as the complete gas stream cross section. The hotreacted gas mixture then flows for a significant distance simultaneouslyin contact and heating the partly melted bath and the furnace wallswhich, in turn, continuously agitate the bath and pass on this wall heatfrom post-combustion into the bath when rotating under it. The inventionthus provides the clear advantage of increasing PCD and HTE over priorart processes, for example, electric-arc furnace and oxygen converterprocess technologies.

[0069] When the carrier gases contain substantial quantities ofcombustibles, two separate gas stream oxygen injection jets can beincluded, one jet such as in FIG. 7 focused on carrier gases and anyaccompanying hot reducing gases evolved from jet 64 and the other, suchas in FIG. 8 providing more uniform coverage of the gas stream crosssection for post combustion of CO evolved from the carbon boil of C andresidual FeO contained in the hot reduced iron. Continuous off-gasanalysis of the exited gas stream then enables adjustment of theinjection location and operating parameters for this additional oxygen.Gas stream injected oxygen may also be applied for combustion of fuelfrom burners 19, 20. For example, burner 20 could be fired fuel-rich,minimizing refining zone 18 oxidation as a side benefit, with the excessfuel then combusted by gas stream injected oxygen within zone 12, overand above that required for foregoing purposes (1)+(2). Charge endburner 19 and gas stream oxygen lances 160 can also be adapted foradjustable longitudinal positioning, for example, juxtaposed and carriedby an assembly substantially identical to that for lance 63, thusproviding means to adjust the distribution of combustion reactions andheat release within zone 12. For example, referring to FIGS. 1 and 2,with nozzle 34 and jet 64 traversing between Lmin and Lmax, the burner19 nozzle could be located just short of Lmax and lance 143 nozzle justbeyond Lmin. Adjusting these locations during operation and observingthe effect on the temperature and composition of gases 33 enables themost effective positions to be established and maintained. Many otherfiring variations and combinations are obviously available.

[0070] Bath oxygen injection lance nozzles characteristically operate atrelatively high pressures and velocities in order to obtain good bathpenetration and agitation, must often at supersonic velocity accordingto known parameters in the art of bath oxygen injection, and generallyuse high-purity cryogenic oxygen to avoid nitrogen pickup in the bath.Gas stream injected oxygen is most effective at much lower pressure andvelocity, also to avoid unwanted bath and slag oxidation reactions anderosion of refractories. Since bath gas-liquid mixing is not involved,lower oxygen purity, such as characteristic of molecular-sieve typeoxygen generation, is also suitable. When utilizing at least 80 per centpure oxygen for combustion and injection, average longitudinal hot gasstream velocities along melting zone 12 are moderate, typically about 15miles per hour of the hot low-density gases, and usually within a rangeof 10 to 30 miles per hour. For a nozzle such as FIG. 8, a nozzlepressure drop of 1 psi (27.7 in. water column) creates a nozzle exitvelocity of about 150 miles per hour for the annular curtain of oxygen,as typically adequate to obtain good mixing with the gas stream out tothe stream perimeter. A 7 in. water column pressure drop translates toabout 75 miles per hour exit velocity which can also be suitablyeffective, thus operating pressures can vary considerably, but wouldusually be less than 5 psi, whereas bath oxygen injection nozzles wouldoperate in a much higher pressure range.

[0071] Group B processes lack a ready carrier gas for bath solidsinjection and natural gas, as commonly available by pipeline at highpressure, is an obvious option. Because of the high calorific value,however, the volume of natural gas required for carrier gasesapproximates that for the total melting heat requirement for zone 12.Whereas longitudinal traversing of lance 64 is an advantage consideringmass transfer and charge distribution, when acting as the principalsource of melting heat, it would be at least partially disruptive ofheat and hot gas distribution within zone 12. Pressurizing exhaust gases112 is another option, as are inert gases or CO₂ as carrier gases. Againconsidering Group A, hot reducing gases 5 would typically supply on theorder of half the melting zone 12 heat requirement, potentially alsosomewhat disruptive. Dewatered and recirculated top gases 50, at aboutone-quarter or less applied as in FIG. 7 is perhaps a cost-effective andpractical compromise selection for Group A. Melting heat requirementsdecrease with increasing percentages of carbon in the hot reduced iron.They increase as the percentage of scrap or other metallic charge 14 isincreased such as by conveyor 13, increasing the tolerance for highercarrier gas combustibles.

[0072] Hot reduced iron and additive transfer operating parametersfollow the natural laws and known principles governing pneumatic solidsconveying, solids fluidization and injection into liquid baths. Theminimum gas velocity within duct 62 clearly must exceed the saltationvelocity. The ratio of mass of hot reduced iron to mass of carrier gasis typically 15-20 but can range from as low as 5 to higher than 30,such as in the course of dense-phase transfer of relatively fine-sizedpieces, as characteristic of fluidized bed hot-reduced iron or ironcarbide. The velocity ofjet 64 is influenced by the desired depth ofbath penetration which, because the mass ratio of carrier gas to solidsis quite low, depends mainly upon the flow rate and velocity of thesolids. Slag separation and creation of a minimum cavity in the bathsurface would usually require a vertically downward component of solidsvelocity exceeding about 20, and typically 30 to 60, miles per hour atbath entry. Nozzle 34 can be straight or can be converging or of Venturitype to increase penetration, or diverging to increase bath areacoverage. A typical example velocity of transfer and injection wouldinclude a carrier gas flow velocity of 50 miles per hour, projecting aflow of 60 short tons per hour of hot reduced iron through a 6-inchdiameter transfer duct and nozzle into the partially melted metal bath32. Since hot reduced iron or iron carbide is abrasive, abrasion withintransfer duct 62 and lance 63 accelerating rapidly with increasingvelocity, relatively low velocities are favored to reduce maintenance,but also selected to realize consistent immersion of reduced iron piecesin bath 32.

[0073] Although venturi eductors for pneumatic solids conveying areusually characterized by a relatively high ratio of carrier gas tosolids, which can be a serious disadvantage if applied as feeders forthe subject pneumatic transfer and injection application, they can offera viable option in cases when reduction and melting are close together,with the gas-solid reduction zone positioned at a significantly higherelevation than the melting zone. FIGS. 10 and 11 present a variation ofthe flowsheet of FIG. 5 illustrating such an application, wherein thefine-sized materials are screened out by a trommel 172 comprising acylindrical section of the rotary reactor inside walls, rather than by avibrating screen. The oversized reduced pellets 99 pass through a funnelchute 173, then drop vertically inside down-pipe 174 feeding the inletof eductor 175, incorporating carrier gas nozzle 176, venturi throat 177and discharge pipe 178 comprising the inlet line to the solids injectionlance 63. In the illustrated example, nozzle 176 is supplied withcarrier gas by a high-temperature blower 179 including a suction inletduct 180 withdrawing hot carrier gas from within the gas-solid reductionzone.

[0074] Eductor inefficiency and high dilution ratio is related to therequirement to accelerate solid particles or pellets from aclosely-packed essentially stationary position, whereas the reduced ironpellets in FIGS. 10 and 11 are already moving at substantial velocity inthe conveying direction at entry into eductor 175. Gravity is theprincipal force acting on the reduced iron pellets dropping throughdown-pipe 174, according to the well known relationship velocity=2 gswhen S is the distance dropped, tempered only by resistance of gases,side-wall friction and directional changes within the pipe. For example,a 4-meter free fall results in a velocity about 20 miles per hour, ornearly half that of a typical injection velocity. Such solid inletvelocities entering the eductor substantially decrease the carrier gasvolume and pressure requirements and, accordingly, transfer duct andlance nozzle diameters.

[0075] Example parameters for a 20 ton-per-hour system may beillustrated as follows: Parameter Target Range Vertical drop 12 ft.10-15 ft. Down-pipe diameter 3 in. 2.5-3.5 in. Carrier-gas nozzlediameter 1 in. 0.8 -1.2 in. Venturi throat diameter 2 in. 1 .8-2.5 in.Carrier gas pressure 2 psig 1.5-3 psig. Transfer duct diameter 4 in.3.5-4.5 in. Transfer duct velocity 4000 ft.per.min. 3500-4500 ft.min.

[0076] A very large number of modifications and variations to theprocess for direct iron and steelmaking are available and obvious tothose skilled in the art. For example, referring to type B processflowsheet FIGS. 5, 6 and 10, the pneumatic charge transfer and injectionsystem depicted in any one is also applicable in either of the othertwo. Other variations could include charging all of the solid reductantand sulphur-absorbent materials for rotary kiln reduction as in FIGS. 5and 6, as a constituent of the pellets, eliminating the requirement forscreening out excess coal, ash and lime-dolomite, with process then verysimilar to the FIG. 6 rotary hearth reduction, except for the type ofgas-solid reaction zone equipment. Alternatively, with all or a majorportion of the reductant charged as discrete particles, the entiremixture could still be passed on into zone 12 also without screening, toyield a high-carbon pig iron hot metal product, accompanied by a greaterportion of the melting heat in the gas-solid-liquid melting zonefurnished by the hot solid carbonaceous material transferred with thecharge. These are only a few of the many variations and equivalenciesavailable without departing from the scope of the invention defined inthe appended claims.

I claim:
 1. An apparatus for making iron and steel directly from ironoxides comprising a reduction reactor containing a gas-solid reductionzone adapted for reducing iron oxides containing pieces yielding hotsolid reduced iron pieces, in communication with an elongate rotaryfurnace containing a gas-solid-liquid melting zone adapted for meltingsaid hot solid reduced iron, by way of a transfer conduit for conductingsaid hot reduced iron pieces from said reduction zone to said meltingzone, which comprises: a pneumatic conveyor duct along at least thesection of said transfer conduit preceding the delivery end of saidtransfer conduit employing pressurized carrier gases entraining andconveying said hot reduced iron pieces; at least one solids injectionlance connected to said pneumatic conveyor duct, said lance beingdirected through an annular end opening of said rotary furnace into thehot gas stream within said melting zone with a nozzle adapted foremitting a jet of said hot reduced iron and carrier gas downwards intosaid partially melted metal bath.
 2. An apparatus according to claim 1also comprising lance traversing means adapted for traversing said jetlongitudinally backwards and forwards along said melting zone.
 3. Anapparatus according to claim 1 or 2 wherein said reduction reactor isselected from the group comprising a shaft furnace and a fluidized bedreactor adapted to percolate pressurized hot reducing gases in contactwith said iron oxides containing pieces within said gas-solid reactionzone and exhaust reacted top gases, which includes pressurizingcompressor means adapted to compress and re-pressurize said top gases,and also includes a conduit for a portion of said top gases with flowcontrol valve means adapted to introduce said top gas portion into saidpneumatic transfer duct as carrier gases for transfer and injection ofsaid hot reduced iron.
 4. An apparatus according to claim 1 or 2 whereinsaid reduction reactor is selected from the group comprising a shaftfurnace and a fluidized bed reactor adapted to percolate pressurized hotreducing gases in contact with said iron oxides containing pieces withinsaid gas-solid reaction zone, including discharge valve means adapted toallow passage of a controlled flow of said pressurized hot reducinggases from said reduction reactor together with said hot reduced ironinto said transfer duct to comprise at least a portion of said carriergases for transfer and injection of said hot reduced iron.
 5. Anapparatus according to claim 1 or 2 wherein said reduction reactor isselected from the group comprising a shaft furnace and a fluidized bedreactor adapted to percolate pressurized hot reducing gases in contactwith said iron oxides containing pieces within said gas-solid reactionzone which includes a reducing gas generator fired by at least one inletfor fresh hydrocarbons and at least one inlet for fresh oxygen adaptedto effect partial combustion within said generator forming reducinggases CO and H₂ for introduction into gas-solid reaction zone withinsaid reduction reactor.
 6. An apparatus according to claim 1 whereinsaid reduction reactor is selected from the group comprising a rotarykiln and a rotary hearth furnace adapted for introducing solidcarbonaceous reductant into said gas-solid reduction zone and heatingsaid iron oxides and reductant for reaction at approximate ambientpressure, which includes an exhaust transfer duct adapted fortransferring hot exhaust gases from said rotary furnace into saidreduction reactor.
 7. An apparatus according to claim 1 or 2 whereinsaid reduction reactor is selected from the group comprising a rotarykiln and a rotary hearth furnace adapted for introducing solidcarbonaceous reductant into said gas-solid reduction zone and heatingsaid iron oxides and reductant for reaction at approximate ambientpressure, including a screen substantially closed from the outsideatmosphere adapted for separating and discharging relatively fine-sizedexcess carbonaceous reductant whilst retaining relatively coarse-sizedhot reduced iron pieces, in combination with a pressurizing valveeffecting transfer of said hot reduced iron pieces into said transferduct simultaneously substantially preventing transfer of saidpressurized carrier gases into said reduction reactor.
 8. An apparatusaccording to claim 1 or 2 wherein said reduction reactor is selectedfrom the group comprising a rotary kiln and a rotary hearth furnaceadapted for introducing solid carbonaceous reductant into said gas-solidreduction zone and heating said iron oxides and reductant for reactionat approximately ambient pressure which includes an eductor comprising acarrier gas nozzle, venturi throat and discharge pipe comprising theinlet line to said transfer duct and injection lance, adapted forreceiving said hot reduced iron from a down-pipe, entraining said hotreduced iron by carrier gas for projection along said transfer ductthrough said lance and nozzle into said bath.
 9. An apparatus accordingto claim 1 or 2 wherein said reduction reactor is selected from thegroup comprising a rotary kiln and rotary hearth furnace adapted forintroducing solid carbonaceous reductant into said gas-solid reductionzone and heating said iron oxides and reductant for reaction atapproximately ambient pressure which includes a lockhopper adapted forcyclically receiving said hot reduced iron from said reactor atapproximately atmospheric pressure, then pneumatically pressurizing anddischarging under pressure into a continuously pressurized lockhopperadapted for feeding said hot reduced iron into said transfer duct forprojection through said lance and nozzle into said bath.
 10. Anapparatus according to claim 1 or 2, also including an oxygen-injectionlance adapted for post combustion of CO evolved from said bath therebyforming CO₂ prior to exit of hot combustion products from said reactorby way of said annular end openings.
 11. An apparatus according to claim1 or 2 including an oxygen injection lance comprising a water-cooledouter pipe and an inner pipe terminating in a distribution control discdefining an annular slit opening between the exit end face of said innerand outer pipes and the back face of said disc, adapted to emit acurtain of oxygen radially outwards transversely across the gas streamof hot furnace gases.
 12. An apparatus according to claim 1 or 2 whichalso comprises an external vacuum vessel having a siphon tube adaptedfor projection through an annular end opening of said rotary furnacedown into said metal bath for discharging liquid iron and steel fromsaid furnace.
 13. An apparatus according to claim 1 or 2 wherein saidrotary furnace also includes a gas-liquid refining zone and a dischargeend burner directed into said refining zone adapted to control the metalrefining temperature essentially independently of the heat requirementsfor melting.
 14. An apparatus according to claim 1 or 2 wherein saidrotary furnace also includes a gas-liquid refining zone and a dischargeend burner directed into said refining zone; a charge end burnerdirected into said melting zone; an oxygen lance directed into saidmelting zone and exhausting means effecting flow of said gas streamwithin said furnace from said refining zone through said melting zoneexiting through annular charge opening.